The present invention relates to a bidirectional vacuum valve interposed between a vacuum chamber and a vacuum pump when evacuating the vacuum chamber.
Up to now, to evacuate a chamber used in such processes as the manufacture of semiconductors or the like, an arrangement shown in FIG. 8 has been used. In this arrangement, a chamber (101) is connected to a vacuum pump (102) by a pipe (103), and the vacuum pump draws air out of the chamber. However, since there is only one vacuum valve (104) between the vacuum pump (102) and the vacuum chamber (101), the rapid and forceful evacuation that occurs when the valve is opened causes turbulence in the vacuum chamber (101) and the pipe (103), stirring up particles such as dusts that are detrimental to the process.
This disturbance of particles can be prevented by modifying the arrangement to give the arrangement shown in FIG. 9. The modification consists of the addition of a bypass line (106) provided with a small-diameter valve (105) to bypass the large-diameter valve (104) in the main vacuum line. Evacuation takes place while simultaneously controlling the two vacuum valves, creating a vacuum step by step. First the small-diameter valve (105) is opened, and the vacuum pump (102) evacuates the vacuum chamber (101) and the pipe (103) to several Torr.
At a vacuum of several Torr, there are not enough particles to be stirred up, and the large-diameter valve (104) can now be fully opened, allowing air to be drawn out of the vacuum chamber stably. However, operating the small-diameter valve (105) and large-diameter valve (104) with a controller causes two problems: control is very complicated and the cost is high. And if the valves are operated manually, misoperation may occurs.